1. Field of the Invention
The invention relates to a driveline for a multi-axle vehicle.
2. Description of Related Art
The invention is suitable for use in 6xc3x976, 8xc3x978, and 10xc3x9710 vehicle drive lines. For example, an 8xc3x978 vehicle has four driven axles, each incorporating a differential unit that in turn drives two wheel sets, one at each side of the vehicle. It is known in practice to distribute the drive power from the engine through the main transmission gearbox via a propeller shaft to a central torque transfer case incorporating a differential unit that splits the drive between the front and the rear of the vehicle. From the central torque transfer case, a first output drive goes via a propeller shaft towards the front of the vehicle to a front torque transfer case incorporating a differential unit that splits the drive between the first and the second axle of the vehicle. Also, from the central torque transfer case, a second output drive goes via propeller shaft towards the rear of the vehicle to a rear torque transfer case incorporating a differential unit that splits the drive between the third and fourth axle of the vehicle.
In known applications, these three torque transfer cases with their associated differential units take up room that would otherwise be available for useful cargo or equipment. It is known practice to integrate the front and rear torque transfer cases and associated differentials with the second and third axle differential units respectively of an 8xc3x978 vehicle and the close-coupled assembly may be termed xe2x80x9ca through-drive axlexe2x80x9d. Frequently, the input shaft to the through-drive axle in has an axis perpendicular to and vertically displaced from the axle centerline. The drive is split in an inter-axle differential unit and the through-drive to the next axle is on the same axis as the input shaft. The drive to the local axle differential is transmitted through parallel axis gears to allow for the vertical displacement of the input shaft from the axle centerline. In an 8xc3x978 vehicle with this drive line layout, the central torque transfer case and the front and rear torque transfer mechanisms and their associated differentials all lie between the second and third axles of the vehicle. This can cause a problem if it is desirable that the second and third axles be closely spaced or if, for example, space must be reserved for equipment such as a weapon turret. Also, because the through-drive from the second axle to the first or front axle is on an axis that is vertically displaced from the axle centerline, the propeller shaft between the axles is at an angle that may be excessive, particularly if the axles are closely spaced. Similarly, the propeller shaft angle between the third and fourth axles may be excessive.
The present invention is directed towards overcoming these problems.
According to the invention, there is provided a driveline for a vehicle incorporating a through-drive axle unit which is a close-coupled assembly comprising a torque transfer mechanism with associated differential unit and an axle differential unit in which an output shaft of the through-drive is on substantially the same axis as an input pinion to the axle differential unit. Advantageously the present inventior provides a through-drive unit which has means for dropping the drive first and then splitting the drive. This is in contrast to conventional through-drive units which typically split the drive first and then drop a first drive to one axle and angulate a second drive via a propeller shaft with universal joints to another axle.
In one embodiment of the invention the through-drive axle unit has a drive input shaft, gearing for dropping the drive downwardly from the drive input shaft to the transfer mechanism differential unit for splitting the drive, said transfer mechanism differential unit having a first output driveably connected to the axle differential unit and a second output shaft for onward drive transmission.
In one embodiment of the invention the vehicle driveline includes:
a torque transfer mechanism with an associated first differential unit,
said first differential unit having an input for connection to a drive means,
said first differential unit having a first output and a second output,
said first output being driveably connected to an output shaft for onward drive transmission,
said second output being driveably connected through an input pinion to an axle differential unit,
said output shaft and said input pinion being on substantially the same rotational axis.
In another embodiment, the invention provides a driveline for a vehicle incorporating an integrated transfer box and through-drive axle unit which is a close-coupled assembly including two torque transfer mechanisms with two associated differential units and an axle differential unit which are driveably interconnected.
In another embodiment the integrated transfer box and through-drive axle unit includes a drive input, means for dropping the drive, means for splitting the drive into a first drive output and a second drive output, the first drive output for onward drive transmission, means for dropping the second drive output means for splitting the second drive output into first and second outputs, the first output for onward drive transmission and the second output connecting to an axle differential unit. Preferably the means for dropping the drive comprises gearing.
In a further embodiment said integrated transfer box and through-drive axle unit includes:
a drive input shaft,
the drive input shaft being driveably connected to a first differential unit,
the first differential unit having a first output and a second output,
the first output being driveably connected to a first output shaft for onward drive transmission,
the second output being driveably connected to a second differential unit having a first output and a second output,
the second differential unit first output being driveably connected to a second output shaft for onward drive transmission,
the second differential unit second output being driveably connected to an axle differential unit having first and second drive outputs for connection to wheels of a vehicle.
In another embodiment the first output of the second differential unit is on substantially the same rotational axis as an input pinion to the axle differential unit.
In another embodiment the second output of the first differential unit is driveably connected to the second differential unit through a parallel axis gear pair.
In a further embodiment, said integrated transfer box and through-drive axle assembly includes first and second torque transfer mechanisms with their two associated differential units and an axle differential unit and is associated with a second axle from the front of the vehicle, takes its drive input from the vehicle engine via a main change-speed gearbox and a drop-box, has a first output from the first torque transfer mechanism towards the rear of the vehicle which drives the rear two axles through a through-drive axle unit located at a third axle from the front of the vehicle, has a second output from the first torque transfer mechanism towards the front of the vehicle which drives the front two axles through a second torque transfer mechanism which has one output close-coupled with an axle differential unit of the second axle and a second output towards the front of the vehicle to a propeller shaft which drives an input shaft of a front axle differential.
In another aspect, the invention provides a through drive axle unit for a vehicle driveline including:
a drive input shaft,
the drive input shaft being drivably connected to a first differential unit,
the first differential unit having a first output and a second output,
the first output being drivably connected to an output shaft for onward drive transmission,
the second output being drivably connected to an axle differential unit having first and second drive outputs for connection to wheels of a vehicle.
In a preferred embodiment, the output shaft is on substantially the same axis as an input pinion to the axle differential unit.
In a further aspect, the invention provides an integrated transfer box and through-drive axle unit for a vehicle driveline, including:
a drive input shaft,
the drive input shaft being drivably connected to a first differential unit,
the first differential unit having a first output and a second output,
the first output being drivably connected to a first output shaft for onward drive transmission,
the second output being drivably connected to a second differential unit,
the second differential unit having a first output and a second output,
the second differential unit first output being drivably connected to a second output shaft for onward drive transmission,
the second differential unit-second output being drivably connected to an axle differential unit having first and second drive outputs for connection to wheels of a vehicle.
In a preferred embodiment, the first output of the second differential unit is on substantially the same axis as an input pinion to the axle differential unit.
In another embodiment, the second output of the first differential unit is drivably connected to the second differential unit through a parallel axis gear pair.